Difference between revisions of "De Vahl Davis natural convection test"
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for (auto c : bottom) T2[c] = op.neumann(T2, c, vec_t{0, 1}, 0.0); | for (auto c : bottom) T2[c] = op.neumann(T2, c, vec_t{0, 1}, 0.0); | ||
} | } | ||
| + | </syntaxhighlight> | ||
| + | |||
| + | Snippet of code for explicit pressure correction scheme. Note that the solution of heat equation is the same as in above example | ||
| + | |||
| + | <syntaxhighlight lang="c++" line> | ||
| + | |||
| + | for (int step = 0; step <= O.t_steps; ++step) { | ||
| + | time_1 = std::chrono::high_resolution_clock::now(); | ||
| + | // Explicit Navier-Stokes computed on whole domain, including boundaries | ||
| + | // without pressure -- Fraction step | ||
| + | int i; | ||
| + | #pragma omp parallel for private(i) schedule(static) | ||
| + | for (i = 0; i < all.size(); ++i) { | ||
| + | int c = i; //interior[i]; | ||
| + | v_2[c] = v_1[c] + O.dt ( | ||
| + | O.mu / O.rho * op.lap(v_1, c) | ||
| + | - op.grad(v_1, c) * v_1[c] | ||
| + | + O.g * (1 - O.beta * (T_1[c] - O.T_ref))); | ||
| + | } | ||
| + | // Pressure correction | ||
| + | VecXd rhs_pressure(N + 1, 0); //Note N+1, +1 stands for regularization equation | ||
| + | rhs_pressure(N) = 0; // = 0 part of the regularization equation | ||
| + | #pragma omp parallel for private(i) schedule(static) | ||
| + | for (i = 0; i < interior.size(); ++i) { | ||
| + | int c = interior[i]; | ||
| + | rhs_pressure(c) = O.rho / O.dt * op.div(v_2, c); | ||
| + | } | ||
| + | #pragma omp parallel for private(i) schedule(static) | ||
| + | for (i = 0; i < boundary.size(); ++i) { | ||
| + | int c = boundary[i]; | ||
| + | rhs_pressure(c) = O.rho / O.dt * v_2[c].dot(domain.normal(c)); | ||
| + | } | ||
| + | |||
| + | VecXd solution = solver_p.solve(rhs_pressure); | ||
| + | alpha = solution[N]; | ||
| + | VecXd P_c = solution.head(N); | ||
| + | |||
| + | // veclocity correction due to the pressure correction | ||
| + | #pragma omp parallel for private(i) schedule(static) | ||
| + | for ( int i = interior) v_2[c] -= O.dt / O.rho * op.grad(P_c, c); | ||
| + | |||
| + | v_2[boundary] = 0; // force boundary conditions | ||
| + | |||
</syntaxhighlight> | </syntaxhighlight> | ||
Revision as of 09:55, 12 March 2018
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Intro
The classical de Vahl Davis benchmark test is defined for the natural convection of the air ($\Pr =0.71$) in the square closed cavity (${{\text{A}}_{\text{R}}}=1$). The only physical free parameter of the test remains the thermal Rayleigh number. In the original paper [1] de Vahl Davis tested the problem up to the Rayleigh number ${{10}^{6}}$, however in the latter publications, the results of more intense simulations were presented with the Rayleigh number up to ${{10}^{8}}$. Lage and Bejan [2] showed that the laminar domain of the closed cavity natural convection problem is roughly below $\text{Gr1}{{\text{0}}^{9}}$. It was reported [3, 4] that the natural convection becomes unsteady for $\text{Ra}=2\cdot {{10}^5}$. Here we present a MLSM solution of the case.
\begin{equation} \text{Ra}\text{=}\,\frac{\left| \mathbf{g} \right|{{\beta }_{T}}\left( {{T}_{H}}-{{T}_{C}} \right){{\Omega }_{H}}^{3}{{\rho }^{2}}{{c}_{p}}}{\lambda \mu } \end{equation} \begin{equation} \text{Pr}=\frac{\mu {{c}_{p}}}{\lambda } \end{equation}
[1] de Vahl Davis G. Natural convection of air in a square cavity: a bench mark numerical solution. Int J Numer Meth Fl. 1983;3:249-64.
[2] Lage JL, Bejan A. The Ra-Pr domain of laminar natural convection in an enclosure heated from the side. Numer Heat Transfer. 1991;A19:21-41.
[3] Janssen RJA, Henkes RAWM. Accuracy of finite-volume disretizations for the bifurcating natural-convection flow in a square cavity. Numer Heat Transfer. 1993;B24:191-207.
[4] Nobile E. Simulation of time-dependent flow in cavities with the additive-correction multigrid method, part II: Apllications. Numer Heat Transfer. 1996;B30:341-50.
.
Figure 1: Scheme of the de Vahl Davis benchmark testCode
The snippet of the openMP parallel MLSM code for an explicit ACM method with CBS looks like: (full examples, including implicit versions, can be found under the examples in the code repository Main Page).
1 v2[boundary] = vec_t{0.0, 0.0};
2 T2[left] = O.T_cold;
3 T2[right] = O.T_hot;
4 //Time stepping
5 for (int step = 0; step <= O.t_steps; ++step) {
6 for (int i_count = 1; i_count < _MAX_ITER_; ++i_count) {
7 // Navier Stokes
8 for (auto c : interior) {
9 v2[c] = v1[c] + O.dt * (-1 / O.rho * op.grad(P1, c)
10 + O.mu / O.rho * op.lap(v1, c)
11 - op.grad(v1, c) * v1[c]
12 + O.g * (1 - O.beta * (T1[c] - O.T_ref)));
13 }
14
15 //Speed of sound
16 Range<scal_t> norm = v2.map([](const vec_t& p) { return p.norm(); });
17 scal_t C = O.dl * std::max(*std::max_element(norm.begin(), norm.end()), O.v_ref);
18 // Mass continuity
19 Range<scal_t> div_v;
20 for (auto c:all) {
21 div_v[c] = op.div(v2, c);
22 P2[c] = P1[c] - C * C * O.dt * O.rho * div_v[c] +
23 O.dl2 * C * C * O.dt * O.dt * op.lap(P1, c);
24 }
25 P1.swap(P2);
26 }
27
28 //heat transport
29 for (auto c : interior) {
30 T2[c] = T1[c] + O.dt * O.lam / O.rho / O.c_p * op.lap(T1, c) -
31 O.dt * v1[c].transpose() * op.grad(T1, c);
32 }
33 for (auto c : top) T2[c] = op.neumann(T2, c, vec_t{0, -1}, 0.0);
34 for (auto c : bottom) T2[c] = op.neumann(T2, c, vec_t{0, 1}, 0.0);
35 }
Snippet of code for explicit pressure correction scheme. Note that the solution of heat equation is the same as in above example
1 for (int step = 0; step <= O.t_steps; ++step) {
2 time_1 = std::chrono::high_resolution_clock::now();
3 // Explicit Navier-Stokes computed on whole domain, including boundaries
4 // without pressure -- Fraction step
5 int i;
6 #pragma omp parallel for private(i) schedule(static)
7 for (i = 0; i < all.size(); ++i) {
8 int c = i; //interior[i];
9 v_2[c] = v_1[c] + O.dt (
10 O.mu / O.rho * op.lap(v_1, c)
11 - op.grad(v_1, c) * v_1[c]
12 + O.g * (1 - O.beta * (T_1[c] - O.T_ref)));
13 }
14 // Pressure correction
15 VecXd rhs_pressure(N + 1, 0); //Note N+1, +1 stands for regularization equation
16 rhs_pressure(N) = 0; // = 0 part of the regularization equation
17 #pragma omp parallel for private(i) schedule(static)
18 for (i = 0; i < interior.size(); ++i) {
19 int c = interior[i];
20 rhs_pressure(c) = O.rho / O.dt * op.div(v_2, c);
21 }
22 #pragma omp parallel for private(i) schedule(static)
23 for (i = 0; i < boundary.size(); ++i) {
24 int c = boundary[i];
25 rhs_pressure(c) = O.rho / O.dt * v_2[c].dot(domain.normal(c));
26 }
27
28 VecXd solution = solver_p.solve(rhs_pressure);
29 alpha = solution[N];
30 VecXd P_c = solution.head(N);
31
32 // veclocity correction due to the pressure correction
33 #pragma omp parallel for private(i) schedule(static)
34 for ( int i = interior) v_2[c] -= O.dt / O.rho * op.grad(P_c, c);
35
36 v_2[boundary] = 0; // force boundary conditions
Results
Following video shows evolution of temperature and velocity magnitude for the $Ra=10^8$ case.
In below galley you can find temperature contour plots, velocity magnitude contour plots, v_max and average hot side Nusselt number convergence behavior. The reference values are from:
- [a] de Vahl Davis G. Natural convection of air in a square cavity: a bench mark numerical solution. Int J Numer Meth Fl. 1983;3:249-64.
- [b] Sadat H, Couturier S. Performance and accuracy of a meshless method for laminar natural convection. Numer Heat Transfer. 2000;B37:455-67.
- [c] Wan DC, Patnaik BSV, Wei GW. A new benchmark quality solution for the buoyancy-driven cavity by discrete singular convolution. Numer Heat Transfer. 2001;B40:199-228.
- [d] Šarler B. A radial basis function collocation approach in computational fluid dynamics. CMES-Comp Model Eng. 2005;7:185-93.
- [e] Kosec G, Šarler B. Solution of thermo-fluid problems by collocation with local pressure correction. Int J Numer Method H. 2008;18:868-82.
